Transformer with variable secondary reactance



E. FRIES Nov; 19, 1946.

Filed June 14, 1943 2 Sheets-Sheet 1 E. FRIES Nov. 19, 1946.

TRANSFORMER WITH VARIABLE SECONDARY REACTANCE Filed June 14, 1943 2 Sheets-Sheet 2 earsnr enrich W'L TH VAREABL'E @ECQENDAPPZ REACTANCE Fries, @erliiron, Switzerland Application dune id, 1943, Serial No. 490,78? in Switzerland July .6, 1942 (Claims. l. The present invention relates to transformers with variable reactance and is particularly an -plicable to transformers for welding or the like I in the past been. made regulable by inserting iron laminations into the leakage path of the primary magnetic flux, that is in shunt with the main flux path. For heavier sections of the magnetic circuit thin sheets were assembled in a lmown manner to form stacks of laminations. The magnetic forces exerted on these stacks may be very high, in which case they must be mounted very solidly in order to avoid noises and vibrations.

This is not too dificult for a constant reactance which permits of stationary mounting of the stacks. However, if a reactance which is adjustable within a wide range is required, it is necessary to provide a variable air gap in the shunt magnetic path. It is structurally dimcult to provide for adjustment of the air gap between wide limits in a simple and inexpensive manner, if vibrations and noises in the apparatus are to be avoided. Such vibrations are disturbing and may in time lead to the destruction of the appa= ratus.

An object of the present invention is to provide simple means for varying the air gap in the path of the secondary magnetic flux of transformers having a high reactance which is adjustable within wide limits, without producing excessive noises or vibrations.

Another object is to provide in'a transformer with primary and secondary windings, a magnetic core which is inductively coupled with the secondary winding of said transformer only and which is provided. with a variable air gap.

Another object is to provide a unitary structure of a transformer and a reactor, the reactor being inductively coupled with the secondary windings of the transformer only and having an adjustable reluctance.

Another object-is to provide a high reactance transformer having primary and secondary wind ings, a primary core inductively interlinked with the primary and the secondary windings, and a secondary core having a variable reluctance and interlinked with the secondary winding only.

Another object is to provide a transformer and a variable reactor with a. primary winding inductively mounted on the core of said transformer and a secondary winding inductively interlinked coils. The stationary secondary core part has 2 with both the core of the transformer and the variable reactor.

Other objects and advantages will hereinafter appear.

The preferred form of the invention provides transformer cores of rectangular cross section and rectangular coils. The transverse interspaoe between the primary and secondary coil is enlarged on one side and a secondary core with an adjustable air gap and inductively interlinked with the secondary coil only, is inserted into this enlarged space. This leakage or secondary core consists of a. stationary part and a movable part, having an air gap between them. ihe stationary part is fixedly connected with the main transformer core or its support and projects axially into the aforementioned interspace from one end of the coils. The movable part which completes the secondarycore is inserted from the other end. This latter part is arranged to be moved in and.

out of the coil by a simple mechanism in such a manner that the air gap is approximately at the central transverse plane of the coils. In case of a two cell single phase core type transformer the leakage core comprises two opposed U-shaped parts, while for three phase transformers the leakage comprises two opposed E-shaped parts, in which case the increased distance between the primary and secondary coils is preferably ar-= ranged on the narrow side of the rectangular at each pole at least one guide bar and the corresponding movable part is pressed against this bar, but so that it is still possible to slide it relative thereto. The pressure is preferably exerted by spring discs.

The accompanying drawings are illustrative of two embodiments of the invention. In the drawings,

Fig. 1 is a vertical section of the embodiment.

of the invention in a singlephase transformer.

Fig. 2 is a top view and partially a cross-section along the lines 2-2 of Fig. 1.

Fig. 3 is a. side view of a modification of the transformer illustrated in Fig. 1.

Fig. 4 is a front view of Fig. 3, while Fig. 5 is a top view, partially in section along the lines 5-5 of the transformer shown in Figs. 3 and 4.

Referring to Figs. 1 and 2, the same illustrates a single phase transformer having two primary coils I, two secondary coils 2, and a closed main magnetic laminated core 3. The coils are rectangular in shape and the transverse distance between the coils l and 2 is stationary part 5, the center section 6 of which,

is common with one leg of the main core 3. The vertical legs 1 of the stationary part 5 are provided 'at their center with flat magnetic or nonmagnetic guide bars 8 and a movable U-shaped part 9 of the secondary core is arranged to straddle these guide bars and to slide longitudinally thereon. The movable part 9 is provided with insulated bolts l provided with nuts II and interposed spring washers l2 to hold the laminations together and press them against the guide bars. The bolts II) are arranged to move in slots l3 of the guide bars, to permit movement of the part 9 relative to the stationary part and thereby vary air gaps l4 between adjacent limbs of the respective parts.

' To provide for adjustment of the air gap the movable part 9 has fixed thereto a tapped boss l5 which engages a threaded shaft IS. A second tapped boss I! is attached to the core 3. The threads in the twov bosses and the coacting threads of the shaft are in opposite directions, so that upon turning of the shaft It by the handwheel l8 attached to its upper end the movable part 9 is moved toward or away from the stationary part, to thereby vary the air gap I4 and thus the reluctance of the leakage core and the reactance of the secondary coils.

In order to provide for a more gradual adjustment of the leakage reactance the air gap may be arranged as shown at an angle to the direction of movement of the movable part. However the air gap may be of any other desired shape and it may partially be bridged by a magnetic shunt such as the guide bars 8 if they are made of magnetic material.

The apparatus functions in the following manner: When the primary coils are connected to an alternating current source a current flows electromotive force in the secondary coils 2 in the usual manner. If now the circuit of the secondof the secondary magnetic circuit and hence by the length of the air gap I4. It is thus possible by adjustment of the air gap to adjust the secondary terminal voltage for any given current within very wide limits.

Referring now to Figs. 3, 4, and 5, the same illustrates a transformer having a primary closed magnetic core 30 which is fixedly mounted on a support 3i by any suitable means (not shown). The two vertical limbs of the core 30 are each 4 provided with a primary coil 3| and a secondary a 8 of Fig. 1.

coil 32. In one direction the inside cross-sectional dimension of the secondary coil is made considerably greater than the corresponding outside cross-sectional dimension of the coil 3|, to,

provide for a space 83 into which projects the vertical limbs of a secondary core 34 having a stationary U-shaped part 35 and a movable U- shaped part 36. The part 351s fixed to the base 34 and its two limbs are preferably provided at their center with guide bars 31 which are arranged and constructed similarly to the guide bar The movable U-shaped member 38 is preferably arranged similar to the part 9 of Fig. 1, so as to straddle the guide bars 31. The laminations of the member 36 are clamped together and against the guide bars 31 in the manner shown in Fig. 2 for the part 9. A threaded bos 38 is fixed to the center limb of the member 35 and a similar boss 39 to the member 33. The two bosses are threaded in opposite directions and engage cooperating screw threads of a shaft 40 provided with a handwheel M. By turning the handwheel in one direction or the other the member 36 is moved relative to the member 35 in the manner aforedescribed in connection with Figs. 1 and 2 to vary an air gap 42 therebetween.

The entire apparatus is preferably enclosed in a casing of which only a portion of the top is ary coils is closed through a translating device, I

as for instance a welding machine, a current flows in the secondary winding. This current induces a secondary flux which passesthrough the core 3 in a direction opposite to that of the primary flux. An additional flux is induced in the secondary core 4, the two secondary fluxes being so related that they jointly are proportional to the counter electromotive force induced in the secondary winding.

The lower the reactance of the leakage core relative to the reluctance of the main core the greater is the proportion of the total secondary flux which passe through the secondary core. The reluctance of the secondary core is largely determined by the length of the air gap l4 so that by increasing the air gap the secondary flux is reduced and vice versa. Thus by moving the part 9 up and down relative to the part 5 the secondary counter-electromotive force is varied to thereby vary the net or output secondary voltage of the transformer. The secondary or leakage fiux varies with the current flowing in the secondary winding so that for any given adjustment of the air gap l4 the secondary voltage decreases with increasing current, as is desirable for a welding transformer or the like. On the other hand, the open circuit voltage of the transformer is only slightly aflected by the reluctance shown at 43. The shaft 40 extends through the casing and the handwheel 4! is arranged outside thereof. In order to indicate the position of the member 36 an indicator 44 is provided. The same comprises a bracket 45 which is fixed to one of the guide bars 37 or any other stationary part of the apparatus and is provided with a horizontal axle 46. Mounted on said axle is a bell crank lever having an arm 48 which is provided with a roller 49 which engages the top surfaces of the member 36. The bell crank is biased in a counterclockwise direction by a spring 59. A second arm 5! of the bell crank carries a circular segment 62.

The cover 63 is provided with a window 54 through which the circular segment 52 can be observed. The window is provided with a pointer 55. The outer circumference of segment 52 is provided with indicia which may be in terms of the reactance of the secondary circuit or in terms of the welding current for which the reactance is to be adjusted. If the member 36 is moved up and down by operation of the handwheel 4| the bell crank is rotated in a clockwiseor counter= clockwise direction respectively. so that different indicia corresponding to the position of the member appear at the window opposite the pointer 53. In this manner the adjustment of the reactor is facilitated from the outside.

' While the drawings show only a single guide accuse/o What I claim as new and desire to secure by Letters Patent is:

l. A transformer providing for adjustment of its secondary reactance with-in wide limits, comprising, a closed primary magnetic core, e mi mary winding of substantially rectangular trans verse cross-section inductively mounted on said v core in fixed relation thereto, a econdary winding of substantially rectangular transverse crosssection telescoped over said primary winding and mounted in fixed relation to said primary wind= ing and said core, and having one side of its inner circumferential wall spaced a substantial distance from the outer circmnferential wall of said primary winding, a secondary magnetic core arranged to passaxially through the space be tween said walls of the primary and secondary windings so as to be inductively interlinked with said secondary winding only, said secondary core -comprlsing a part mounted stationary with respect to said windings and another part which is movable relative to said stationary part to interpose a variable air gap in the path of the flux induced in said parts bysaid secondary windlng, said air gap being located near the transverse central plane of said secondary winding, a guide bar fixed to one of said parts, means attached to said other part and arranged to hold the latter in resilient sliding engagement with said bar, and means to reciprocate said movable part on said guide bar for varying the length of said air gap.

2. A single phase transformer providing for adjustment oi its secondary reacta'nce within wide limits, comprising, a. closed rectangular primary magnetic core, a pair of primary and a pair of secondary coils, one of said primary and one of said secondary coils being mounted on one and the other primary and secondary coil being mounted on the other of two opposite sidemember of said rectangular core, said coils being of substantially rectangular transverse cross-section with each secondary coil telescoped over the respective primary coil and having one side of its inner circumferential wall spaced a substantial distance from the outer circumferential wall of the respective primary coil, a rectangular secondary magnetic core arranged with its opposite side members passing axially through the space between said walls so as to be inductively interlinked with said secondary coil only, said secondary core comprising a U-shaped part mounted stationary with respect to said coils and an inverted U-shaped part which is movable relative to said stationary part to interpose vari-- able air gaps between the respective opposed pole faces said parts, and said air gaps being located near the transverse central plane 01 said secondary coils, and means to reciprocat said movable part relative to said stationary part to vary the length of said air gaps.

single phase transformer providing for adjustment of its secondary reactance within wide limits, comprising, a closed rectangular primary magnetic core, a pair of primary and a pair of secondary coils, one of said primary and one oi said secondary coils being mounted on one and the other primary and secondary coil being mounted on the other of two opposite side members oi'seid rectangular core, said coils be lng oi substantially rectangular transverse crosssection with each secondary coll telescoped over the respective primary coil and having one side of its inner circumferential wall spaced a substantial distance from the outer circumferential wall of the respective primary winding, srectangular secondary magnetic core arranged with its opposite side members passing axially through the space between said walls so as to be inductively interlinked with said secondary coll only, said secondary core comprising a U-shaped part mounted stationary with respect to said coil and an inverted U-shaped part which is movable relative to said stationary part to interpose a variable air gap between the respective opposed pole faces of said parts and said air gaps being located near the transverse central plane of said secondary coils, a guide bar fixed to each of the side, members of said stationary part, means attached to the side members of said movable part and arranged to hold the latter in resilient sliding engagement with said bar, and means to reciprocat said movable part relative to said stationary part to vary the length of said air gap.

4. A single phase transformer providing for adjustment of its secondary reactance within wide limits, comprlslng,'a closed rectangular primary magnetic core, a pair of primary and a pair of secondary coils, one Of said primary and one each oi said secondary coils being mounted on one and the other primary andv secondary coil being mounted on the other of two opposite side members of said rectangular core, said' coils being of substantially rectangular transverse cross-section with each secondary coil telescopecl over the respective primary coil and having one side of its inner circumferential wall spaced a substantial distance fromthe outer clrcumieren- I tial wall of the respective primary coll, a rectangular secondary magnetic core arranged with.

its opposite side members passing axially through the space between said walls so as to be inductively interlinked with said secondary coil only, said secondary core comprising a U-shaped part mounted stationary with respect to said coils and an inverted U-shaped part which is movable relative to said stationary part to interpose variable air gaps between the respective opposed pole faces of said parts, and said air gaps being located near the transverse central plane of said secondary coils, and means to move said movable part relative to said stationary part to vary the length of said air gaps, said means comprising a screw tap attached to said stationary part and a screw top attached; to the movable part, said taps having their threads in opposite directions and a shaft provided with threads cooperating with said taps and with a handwheel w ereby rotational said handwheel in opposite directions affords relative movement between said parts to thereby adjust the length of said air gap.

5. A single phase transformer providing for adjustment of its secondary reactance within wide limits, comprising, a closed rectangular primary magnetic core, a pair of primary and a. pair or secondary coils, one of said primary coils and one members passing axially through the space between said walls so as to be inductively interlinked with said secondary coil only, said second-g ary core comprising a U-shaped part mounted stationary with respect to said coil and an inverted U-sh'aped part which is movable relative to said stationary part to interpose a variable air gap between the respective opposed pole faces of said parts, and said air gap being located near the transverse central plane of said secondary coils, a guide bar fixed to each of the side members of said stationary part, means attached to .the side members of said movable part and arranged to hold the latter in resilient sliding engagement with said bar, and means to move said movable part relative to said stationary part to vary the length of said air gaps, said means comprising a screw tap attached to said stationary part and a screw tap attached to the movable part, said taps having their threads in opposit directions, and a shaft provided withthreads cooperating with said taps and with a handwheel whereby rotation of said handwheel in opposite directions affords relative movement between said parts to thereby adjust the length of said air gap.

6. A transformer providing for adjustment of its secondary reactance within wide limits, comprising, a closed primary magnetic core having a plurality of legs, a primary winding for each of said legs and inductively encircling the same, a secondary winding for each of said legs and encircling the same and the respective primary winding and having its inner circumferential wall spaced from the outer circumferential wall of the respective primary winding, a secondary magnetic core having a leg for each of said secondary windings, each of said last named legs being provided with an adjustable air gap and being arranged to pass axially through the space between the walls of the respective primary and secondary windings, and means to vary the length of said air gaps.

'7. A transformerproviding for adjustment of its secondary reactance within wide limits, comprising, a closed magnetic core having a plurality of legs, a primary winding of substantially rectangular transverse cross-section for each of said legs and inductively encircling the same, a secondary winding of substantially rectangular crosssection for each of said legs telescoped over the respective primary winding and having one side of its inner circumferential wall spaced a substantial distance from the outer circumferential wall windings, and means to vary the length of said air gaps.

8.-A transformer providing for adjustment of its secondary reactance within wide limits, com-"'- prising, a closed primary circuit having a plu-' transverse cross-section for each of said legs tele-- scoped over the respective primary winding and having one side of its inner circumferential wall spaced a substantial distance from the outer circumferential wall of the respective primary winding, a secondary magnetic core having a leg in. cluding a variable air gap for each of said secondary windings and being arranged to pass through the space between the respective walls of the primary and secondary windings, said air gaps being located near the transverse central plane of said secondary windings and extending be tween two planar pole faces parallel with each other and at an angle to said plane and means to vary the length of said air gaps.

9. A transformer providing for adjustment of its secondary reactance within wide limits, comprising, a closed primary magnetic core having a plurality of legs, aprimary winding of substantially rectangular transverse cross-section for each of said legs and inductively encircling the same in fixed relation thereto, a secondary winding of substantially rectangular transverse crosssection for each of said legs and telescoped over the respective primary winding and mounted in fixed relation thereto and having one side of its inner circumferential wall spaced a substantial distance from the outer circumferential wall of the respective primary winding, a secondary magnetic core having a leg for each of said secondary windings and arranged to pass axially through the space between the walls of the respectiv primary and secondary windings, said secondary core comprising a part mounted stationary with respect to said windings and another part which is movable relative to said stationary part to interpose variable air gaps in the path of the flux induced in saidparts by said secondary windings, said air gaps being located near the transverse central plane of the respective secondary windings, and means to move said movable part relative to said stationary part to vary the length of said air gaps.

- EDUARD FRIES. 

